A radar device used for a vehicle or other uses radiates a radio wave and receives a reflected signal that is the radio wave reflected by a target to be detected, and detects position information of the targets including a distance, angle, and the like from the information of the received signal. The detected position information may be used as is. But in the case, unintended target may be detected, or a target that should be properly detected may not be able to be detected due to noise or the like.
Therefore, a usual radar device performs a clustering process and a tracking process on obtained information. The clustering process is a process for grouping the signals detected in an detection cycle, and for defining each group (cluster) as a set of signals reflected by one object. For grouping the detected signals, a process for setting ranges of a predetermined shape, and defining a set of signals in each of the ranges as one cluster is performed. As a shape of ranges used for the clustering process (cluster shape), shapes such as circle, ellipse, and rectangle illustrated in FIGS. 8A-8D are often used conventionally.
In the tracking process, a process for comparing a cluster set obtained in the clustering process with positions of all targets that have been obtained so as to determine which target each of the clusters belong to, and based on the determination result, smoothing (averaging) positions for each of the targets and predicting a position next time. Generally, for smoothing or prediction of positions in the tracking process, α-β filter technique or Kalman filter technique are widely used.
Depending on the type of the radar, the radar can output position information (distance/angle) of targets and can also output relative speed information of the target as viewed from the radar (Doppler radar device, for example). However, the relative speed information has not been conventionally output because a processing load increases, and thus it becomes hard to complete all processes within a predetermined time, for example, if the clustering process is performed also using the relative speed information.
A clustering process and tracking process disclosed in Patent Literatures 1 to 3 are known as those performed in conventional radar devices. Patent Literature 1 reports a method for reducing a process for obtaining a correlation between position information obtained in every detection cycle and information of targets that has been obtained in the tracking process. In Patent Literature 1, the shape of clusters that are sets of position information of targets is not specified.
Patent Literature 2 discloses a technique to detect obstacles from captured images obtained by a camera. It is described that a set of candidate points to be detected having their image positions in a predetermined range is defined as one cluster, but the shape of the predetermined range is not particularly defined. In Patent Literature 3, an example where the cluster shape is defined to be rectangular or elliptical is disclosed, but the shape of an area when a size of a plot set is obtained does not matter and the shape is not specified.